The present invention relates to a method of coating a resin solution which is hardened by polymerization.
Conventionally, the slide hopper-type, the extruder-type and the Giesser-type coating apparatus, each equipped with a liquid-spouting slit and/or a liquid-releasing edge, have been employed for the continuous application of a coating liquid onto the surface of a support web. However, the use of these apparatus encounters such a problem that a coating liquid may adhere to the periphery of the liquid-spouting slit and/or the liquid-releasing edge due to its stagnation, wetting and creeping back flow when continuously applied onto the surface of a support web, and solidify there with the lapse of time. When a coating liquid comprises a hardenable resin, this phenomenon causes serious coating streak trouble, and eventually leads to significantly lowered productivity and poor product quality.
The adhering coating liquid, which is hardened by polymerization, is too hard to be removed by washing with water or wiping off with a solvent. Shaving-off with a knife is the only effective way to remove it, but, to avoid a risk that a coating apparatus which is shaped precisely gets scratches, such shaving must be done carefully taking a long period of time.
The coating of a resin solution which is hardened by polymerization is always accompanied by coating streak trouble, that is of a cause entirely different from a similar comet-like longitudinal streak trouble which is caused by the slower flow of solid particles when an ununiform coating liquid obtained by suspending the solid particles is applied. This trouble cannot be avoided by adjusting coating conditions such as the viscosity of a coating liquid or by controlling the fluctuations of a web.